In a large pot, sauté the onion, garlic, and salt in the olive oil until they are transparent.
While the onions and garlic cook, core and chop the tomatoes. Once the alliums are transparent, add the chopped tomatoes. Bring to a boil and simmer for 15-20 minutes, until the tomatoes have broken down.
Position a sieve or food mill over a large bowl and begin to press your hot tomatoes, onions and garlic through it. Once the tomato sauce has been separated from the seeds and skins, return it to the pot and stir in the basil and parsley. Simmer sauce until it is reduced by 1/3 to 1/2.
When you’re about half an hour out from being ready to can, prepare a boiling water bath and 4 quart jars. Place lids in a small saucepan over very low heat to simmer while you prepare the tomatoes.
Take your prepared jars and add 3 tablespoons of bottled lemon juice to the bottom of each jar. Pour the hot tomato sauce into the jars, leaving 1/2 inch headspace.
Wipe the rims, apply lids and rings and process in a boiling water bath for 40 minutes.